Receptor signaling pathways are the subject of widespread research efforts. A better understanding of these signaling pathways will lead to the design of new and more effective drugs in the treatment of many diseases. Of particular interest are the growth factor and related receptor signaling pathways and their role in cell growth and differentiation. Binding of a particular growth factor to its receptor on the cell plasma membrane can stimulate a wide variety of biochemical responses, including changes in ion fluxes, activation of various kinases, alteration of cell shape, transcription of various genes and modulation of enzymatic activities in cellular metabolism.
Growth factors play a role in embryonic development, cancer, atherosclerosis and the responses of tissues to injury. Growth factors are involved in several normal developmental processes as well as in pathological conditions. Many growth factor receptors are tyrosine kinases whose signalling is dependent upon tyrosine phosphorylation of both the receptor and other molecules. Specific phosphorylated tyrosine residues on these receptors recruit soluble intracellular signaling molecules to the complex upon growth factor stimulation, thus initiating the growth factor signaling cascade. The signal can then proceed through a series of steps to the nucleus and other subcellular locations where the final effects of activation by the extracellular ligand are produced. Recruitment of molecules is often carried out by adapter molecules containing only protein-protein interaction domains with no associated enzymatic activity. By examining the molecules that interact with these adapters, important parts of the signaling mechanism can be discovered, monitored and controlled. One such adapter protein is GRB2, a 24 kDa cytosolic adapter protein containing two SH3 domains flanking an SH2 domain, which is known to be involved in linking many important molecules in signal transduction.
Because disregulation of the cellular processes involved in cell growth can have disastrous effects, it is important to understand and gain control over these processes. This requires identifying the participants in the signaling events that lead to mitogenesis and elucidating their mechanism of function. The identification of these participants is important for a wide range of diagnostic, therapeutic and screening applications. In particular, by knowing the structure of a particular participant in a growth factor activation cascade, one can design compounds which affect that cascade, to either activate an otherwise inactive pathway, or inactivate an overly active pathway. Similarly, having identified a particular participant in a growth factor cascade, one can also identify situations where that cascade is defective, resulting in a particular pathological state. The identification of participants in particular growth factor activation cascades is thus of critical importance for screening compounds that affect these cascades and treating a variety of disorders resulting from anomalies in these cascades, both as therapeutic agents and as model systems for identification of compounds which affect the pathway and thus may be useful as therapeutic agents. The present invention meets these and many other needs.